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Re: [TowerTalk] Ground wire impedance

Subject: Re: [TowerTalk] Ground wire impedance
From: K4SAV <>
Date: Wed, 12 Jul 2006 22:14:58 -0500
List-post: <>
Jim Lux wrote:
..."Hmm.. but, if I had four AWG 10 wires laying side by side, that's 
like a 0.4 inch wide by 0.1 inch high strap... i.e. the L should be 0.40 
uH (give or take) for the 10 foot run.  I suspect that 4 AWG16 (roughly 
0.05" diameter) wires spanning half an inch would have about the same 
inductance, and 4 AWG16s is a lot cheaper than a single AWG4, or, 
perhaps, an 0.05x0.5" strip.  As you show in your table, (and you 
mention above) you have to spread over a MUCH wider distance to 
materially reduce the L."...

Without calculating anything, this sounds correct.
..."Where I'm going with this is that there might be some very 
convenient, and inexpensive, ways to get a fairly low inductance 
connection comparable to AWG4, and potentially easier to handle.  For 
instance, there's AWG16 ribbon cable that shows up surplus every once in 
a while.  Or, perhaps, if there's a "deal" on cheap extension cords.  If 
DC resistance isn't the issue, you don't really need the copper mass of 
a big solid chunk.  Something with fairly small copper strands separated 
by plastic, paper, other fillers, can have an impedance for RF and/or 
lightning that's pretty acceptable.  Think of it as quasi Litz wire."...

Maybe. If you are thinking of above ground point-to-point wiring this 
might work OK. If you are thinking buried wires for lightning 
protection, you will lose the ground contact with insulated wire which 
will reduce its effectiveness.  And you can't use uninsulated buried 
stranded without loosing the strand-to-strand contact. Now the next 
interesting question. Will the impedance increase? From the calculations 
in my original table, the INDUCTANCE is the dominate parameter, but that 
was for solid wire.

Unfortunately inductance and skin resistance of stranded-twisted, or 
stranded-braided, or Litz wire is very difficult to calculate when you 
don't have strand to strand contact. There are a number of parameters to 
worry about with these configurations which make it difficult to 
calculate anything, and measurements aren't that easy either.  Most have 
uncontrolled physical configurations (except Litz wire) so you have to 
worry about currents in individual strands getting out of phase with 
other strands. And how is skin resistance effected by currents in 
another conductor immediately next to it? I could guess at the effects, 
but it would just be a guess. If you know of any data, either measured 
or calculated, for inductance or skin resistance of these wire 
configurations I would be interested.

Jerry, K4SAV

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